How to Filter Records with Aggregate Function SUM

Problem:

You need to find rows in which groups have a sum of values in one column less than a given value.

Example:

Our database has a table named company with data in the following columns: id, department, first_name, last_name, and salary.

Let’s find the names of departments that have sums of salaries of its employees less than 7000.

Solution:

SELECT department, SUM(salary)
FROM company
GROUP BY department
HAVING SUM(salary)<7000;

Here’s the result:

Discussion:

To filter records using the aggregate function (the function SUM from earlier), use the HAVING clause. To calculate the sum of values for each group of rows, use the aggregation SUM function. In this query, the column department is calculated with the sum of all salaries of its employees as a group (calculate it with the SUM function with the column salary as an argument). Because you calculate the value for each group of rows (we group rows according to the name of the department), the query has a GROUP BY clause with the name of the column to group rows (in our example, GROUP BY department). The last step is using the aggregate function in the HAVING clause. Remember, HAVING should be put after GROUP BY clause. HAVING contains the condition comparing the value returned by the aggregate function with a given value. From above, it's the salary sums with a value less than 7000 (SUM(salary)<7000). Here, we verify the salary sum in each department is lower than 7000. The query displayed only one department, finance, with salaries of 6550.